The present invention relates to small-molecule compounds that modulate capsid assembly and block hepatitis B virus (HBV) replication with the potential to be used as a monotherapy or in combination with other antivirals for the treatment of chronic HBV infection.
HBV is a small enveloped DNA virus belonging to the Hepadnaviridae family that is distributed worldwide as ten geographically distinct genotypes. Infection with HBV is typically self-limiting in otherwise healthy adults; however, vertical transmission or exposure during early childhood often results in a chronic lifelong infection. Worldwide there are an estimated >400 million individuals chronically infected with HBV that are at risk for complications due to liver disease, including cirrhosis, fibrosis, hepatocellular carcinoma and death. Each year 500,000 to 1 million people die from end stage liver disease as a consequence of HBV infection
The compact HBV genome utilizes four overlapping reading frames to encode the major structural and non-structural proteins: polymerase (F), envelope (S), core (C) and the X protein (X). HBV enters human hepatocytes via receptor mediated endocytosis, following binding of the envelope glycoprotein to its primary receptor, the bile acid transporter sodium taurocholate co-transporting polypeptide (NTCP). Following fusion with the endosome membrane, the capsid is ejected into the cytoplasm and translocated to the nucleus. The partially double-stranded, relaxed, circular HBV genome (RC DNA) is converted to a covalently closed circular DNA form (cccDNA) by host cellular DNA repair mechanisms. The HBV cccDNA serves as the template for RNA polymerase II-dependent transcription of multiple RNA species, including viral mRNAs and the 3.2-kbp pre-genomic RNA (pgRNA). During the maturation process, pgRNA is packaged into capsids along with the HBV polymerase. The pgRNA is then reverse transcribed into a negative-stranded DNA template that is subsequently converted into the partially double-stranded RC DNA species by the polymerase. Mature, enveloped HBV particles containing the RC DNA genome are secreted from the surface of the infected hepatocyte ready to initiate new cycles of infection.
The capsid is composed of 240 copies of the core protein that spontaneously self-assemble through a network of weak inter-subunit interactions. In vitro evidence suggests that a trimer of core dimers initiates the nucleation event that rapidly recruits additional dimers to form the icosahedral core structure (T=4). In addition to its structural role, encapsidation of the pgRNA is an essential step required for HBV DNA synthesis and formation of the mature capsid particle. The core protein also plays an important role in shuttling the RC DNA into the nucleus to initiate and maintain the cccDNA pools and may also play a role in regulating interferon sensitive gene expression. Thus, capsid modulators may have the unique ability to intervene at multiple points in the HBV lifecycle.
Several chemotype series of HBV capsid assembly modulators have been reported in the literature including: phenylpropenamides (PP) (e.g., AT-130), heteroarylpyrimidines (HAP) (e.g. Bay 41-4109), and sulfamoylbenzamides (SBA) (e.g. NVR 3-778). Capsid modulators exert their effects on the assembly process through one of two different mechanisms of action. The HAP series induces the aberrant assembly of large capsid aggregates that subsequently triggers the degradation of the core protein. The PP and SBA series, on the other hand, appear to accelerate capsid assembly resulting in the production of authentic empty capsid particles that have failed to incorporate pgRNA. Assembly modulators representing both mechanisms have demonstrated the ability to reduce HBV DNA levels in mouse models of infection. More recently, NVR 3-778 (SBA) demonstrated clinical proof-of-concept in a Phase 1b clinical trial, resulting in a −1.7 log 10 reduction in HBV DNA following 600 mg bid dosing for 29 days.